Spring Enchantment: Vernal Ponds

One of the many fulfilling things I have the privilege to do as the Managing Director of the Nantucket Field Station is to bring inner city/urban high school students to Nantucket to learn about our habitats, creatures, history, and landscape. With the wet “froggy” weather we have endured over the past week, the island’s treasure trove of vernal ponds, wetlands and bogs are bursting at the seams. So first on our menu of adventure is to go investigate a vernal pond, and who better to go with than the vernal pond protectors of the Nantucket Land Council Executive Director Cormac Collier and Resource Ecologist Emily MacKinnon. Mucking about in waders and seeing first-hand the deep orange, tannin-stained color of these shallow ponds as we search for water beetles, tiny crustaceans, fairy shrimp, and elusive tree frogs is the best way to spend a rainy Saturday.

There is nothing quite like a vernal pool. Vernal ponds are temporary pools of water usually created by spring rains, melt-water from ice and snow, and the associated rising groundwater. These “ephemeral” or fleeting ponds got their name from the Latin word for spring (“vernal”). Some vernal pools can be created by fall rains (autumnal”) and may even persist over the winter. Typically they have no natural outlet or stream for water to drain into or out of the system.

Red Back Salamander

According to the U.S. Environmental Protection Agency’s official vernal pool website www.epa.gov/owow/wetlands/types/vernal.html: “The term vernal pool originally referred only to small, intermittently filled wetlands found in the Mediterranean-type climate of the western United States. Today it is used more broadly to include other small ephemeral wetlands found country-wide.” In Massachusetts, vernal pond habitat is currently defined as areas where water is contained for more than two months in the spring and summer of most years and where no reproducing fish populations are present. So the majority of vernal pools are small, shallow ponds characterized by a lack of fish and by periods of dryness. Vernal pool habitat is extremely important to a variety of wildlife species including some amphibians that breed exclusively in vernal pools, and other organisms such as fairy shrimp, which spend their entire life cycles confined to vernal pool habitat. Many additional wildlife species utilize vernal pools for breeding, feeding and other important functions. Vernal ponds contain many species who either cannot survive predation by resident fish or that have a portion of their life cycle that is dependent on the desiccation function of their surroundings.

Massachusetts was one of the first states to formally recognize vernal ponds and develop regulations protecting them as special habitats of concern. The Massachusetts Division of Fisheries and Wildlife’s Natural Heritage & Endangered Species Program recently released an updated “Guidelines for the Certification of Vernal Pool Habitat” (www.mass.gov/dfwele/dfw/nhesp/vernal_pools/pdf/vpcert.pdf) which lists a description of the two types of species used along with physical criteria to distinguish a vernal pool. They are: “Obligate Species: vertebrate and invertebrate species that require vernal pools for all or a portion of their life cycle and are unable to successfully complete their life cycle without vernal pools. Facultative Species: vertebrate and invertebrate species that frequently use vernal pools for all or a portion of their life cycle, but are able to successfully complete their life cycle in other types of wetlands.”

According to the Vernal Pool Association, in New England, the most easily recognizable obligate species are organisms such as fairy shrimp, mole salamanders, and the wood frog. We do not have mole salamanders here but our trusty State Reptiles and Amphibians list (link below) updated regularly by Jim Cardoza and Peter G. Mirick (Massachusetts Division of Fisheries and Wildlife) lists Spotted Salamanders (Ambystoma maculatum)and Eastern Red-backed Salamander (Plethodon cinereus) as two species of salamanders that we do have roaming the vernal ponds of Nantucket. Our primary obligate species on island and at least a runner-up in any local “coolest creature” contest is the fairy shrimp. Our primary facultative species (and one of the best ways to find these well hidden ponds) is the spring peeper.

If ever a creature was aptly named, the fairy shrimp [Eubranchipus vernalis and the less common E. intricatus] is it—from their upside down swimming behavior (common for all the species in the order Anostraca) and forked white tails to the delicate manner in which the females protect the encysted eggs in a brood pouch. These inch-long crustaceans, whose diaphanous bodies are tinted in varying shades of blue, orange, or yellow, are as ephemeral as their habitat. The shrimp mate and the females lay eggs that fall to the bottom of the pool. The eggs go into suspended animation when the pool dries out, sitting in the sediment for months or years, if necessary, until the pool fills up again. These eggs can even survive ingestion by animals. Once immersed in water, like magic “sea monkeys,” the creatures come to life, breed and die, all in as few as 15 days.

While the fairy shrimp are around, they serve as an important food source for hungry waterfowl and other birds migrating north during the spring. And yes, the similarities to a “Sea Monkey” or brine shrimp are not accidental. Fairy shrimp (Anostraca) are invertebrates that include brine shrimp (Artemia (=Sea Monkeys)). There are about 300 known fairy shrimp species. While a few fairy shrimp species live in salty environments (hence the name brine shrimp), the majority of fairy shrimp live in fresh water like our local friends. The fairy shrimp found in vernal ponds on Nantucket in areas like Squam Swamp are orange in color due to a combination of higher levels of hemoglobin created to accommodate and facilitate oxygen transport in water known for lower oxygen levels and carotenoids in the phytoplankton and microscopic detritus they eat. In the spring, oxygen levels are high and the water temperature is cold, but as temperatures increase and the water level drops (and decomposition increases) the oxygen levels drop. We measured a pH of 4.2 in a vernal pond on May 2nd and a temperature of 15.0 degrees C with lots of oxygen in the water.

The race to complete all the stages in an organism’s life cycle before the pond dries up is also complicated by a delicate and highly orchestrated dance of larval emergence and development observed in many species of vernal-pond-loving insects, dragonflies, salamanders, frogs, and crustaceans. Each group’s appearance is carefully timed to include optimal egg laying, die off or sequestering in the mud, or haul up on land (or into the sky for the dragonflies and mosquitos) before their primary nemesis comes along. The fairy shrimp are an excellent example of this as they come out very early in the sequence of larval development and are gone before too many other predators show up. Several species of salamanders though, are exhibiting die offs due to an inability to escape a pond quickly enough in the tadpole stage before a pond dries up from cutting surrounding trees that provide shade protection from the sun’s rays.

Many people believe (for good reason) that the Father of vernal pool protection, certainly in Massachusetts and with many advocates nation-wide, is Leo P. Kenney. Mr. Kenney is the founder of the Vernal Pool Association and was awarded the 1995 Environmental Law Institute and EPA National Wetlands Award for his vernal pool outreach efforts. His book, co-written with Matthew R. Burne, A Field Guide to the animals of Vernal Pools is the book to use for identifying animals that live in vernal ponds in the Northeast. Other cool species well documented and photographer in the book and lurking in island pools include the caddisfly larvae (drags around a protective casing), predaceous diving beetles, mosquito “wrigglers,” phantom midges, water striders, mayfly and dragonfly larvae, among many other fascinating creatures.

According to the VPA website (www.vernalpool.org/): “The Vernal Pool Association began in 1990 as an environmental outreach project at Reading Memorial High School, Reading, Massachusetts. It is now an independent group of individuals attempting to educate others about vernal pool ecology, the local environment, bio-diversity, and the protection of our resources.”

A key to protecting a vernal pool and properly enforcing any restrictions of development or land use nearby lays in documenting its existence. This is where the vernal pool certification program comes into play. From the VPA website: “Certification is the procedure by which citizens can document the existence of a vernal pool in Massachusetts. The documentation material is submitted to the Natural Heritage & Endangered Species Program which then certifies the vernal pool. When a vernal pool has been certified, it receives automatically any protection afforded to vernal pools under the Wetlands Protection Act. Therefore, in Massachusetts, vernal pools are certified as "existing" by the Natural Heritage & Endangered Species Program based on documentation by citizens. Documentation for vernal pool certification has three components: evidence, maps, and an observation form.” In 2009, NHESP strengthened the rules for identifying a vernal pond by limiting the use of facultative species, thus ensuring that vernal pools were truly vernal pools. On island, the Nantucket Land Council has traditionally been the advocate for documenting our vernal pools and new pools have been discovered in conservation properties such as the Linda Loring Nature Center property off Eel Point road and here at the Nantucket Field Station (protected thanks to the generosity of donors for the Nantucket Conservation Foundation purchase).

Habitat destruction is the major threat to vernal ponds. Often, people mistake seasonally wet areas as "wasteland," and proceed to fill in or drain these critical habitats. Sometimes landowners mistakenly believe that by making a vernal pond permanent (by digging it bigger and deeper) they are increasing the value of the area for wildlife. And diverting groundwater for other uses, whether in filling private ponds or by building culverts in areas not suited for them, can lower groundwater areas and permanently dry up these critical resources. Tree cutting and buffer removal takes away two very important defense mechanisms; the lack of shade and leaves that fall into the pond and provide habitat, hiding spaces, and decompose into usable matter is a primary worry with tree cutting and overly aggressive forestry practices. Vegetated buffer zones around vernal ponds keep silt out of the vernal pond. Excessive silt can fill in a pond and also suffocate the delicate salamander and frog eggs. Sadly, many ponds are filled in, or altered in some way long before they are documented or even known to exist. A vernal pond can be simply a low spot in the summer. It is estimated that in California, perhaps only 7% of the vernal ponds are still intact.

Some states like Kentucky, Ohio, and Pennsylvania have developed procedures for landowners, conservation groups, and school children to “build their own” vernal ponds. Nantucket has its fair share of these natural habitats, but if you live somewhere where vernal ponds are endangered, you might want to check out “A Guide to Creating Vernal Ponds: all the information you need to build and maintain an ephemeral wetland” by Thomas R. Biebighauser. An interesting by-product of habitat loss is the creation of mitigation ponds where developers can pay big bucks to buy “fairy shrimp” credits where shallow pools are nurtured to mitigate for habitat loss at another site. Yes, Virginia, there really is a “fairy shrimp” farm.

Even of more concern are the lower diversity and incidences of mutation observed in many species of animals that live in these habitats. Amphibians are declining world wide due in great part to their ability to absorb chemicals and moisture through their skin. Amphibians are indicator species for pollution and vectors that act as early warning systems. So far, the alarms, have been, well…… alarming, and we’ll discuss those in detail in an upcoming column.

To learn more about vernal ponds, go to the VPA website or read about them in the highly regarded book, Vernal Pools: Natural History And Conservation by aquatic ecologist Elizabeth A. Colburn (formerly with the Massachusetts Audubon for 18 years and currently a staff member of Harvard Forest in Petersham, Massachusetts) and available on Amazon. For more information on vernal ponds and the creatures that live there, you might like: